Rotary drill bits are typically used in drilling through the earth such as in oil field drilling. The body of a drill bit is attached to a drill pipe by a threaded member on the body of the bit. The drill pipe is supported and rotated by a drilling rig. The body of the rotary drill bit typically has three legs, each of the legs having a projecting, conical cutter-receiving journal. Three conical cutters, each having an axially extended recess open at one end, are rotatably mounted on respective journals through the use of interior friction reducing bearings interior to the conical cutters. Each conical cutter has rock cutting teeth or inserts on the surface of the conical cutter. The conical cutters cut through the rock when the weight of the drill pipe above the drill bit and the rotation of the drill pipe causes the conical cutters to independently rotate about their individual journals and to cut through the rock. In order to reduce interior wear of the rotary drill bit, fluid carrying conduits interior to the leg members and extending to the bearings inside the conical cutters, supply lubrication to the bearings. In order to prevent loss of lubricant, typically each conical cutter will have some sort of sealing means to seal in this lubricant. The sealing means, which is located at the open end of the conical cutter recess, also prevents abrasive materials from entering through any space between the base of the journal and the open end of the conical cutter mounted on this journal, inside the conical cutter to the bearings.
Failure of the seal might result in the bearing lubricant escaping and might result in abrasive material migrating into the bearings. Therefore, various prior art patents have taught sealing techniques for rotary drill bits. For example, U.S. Pat. Nos. 4,453,836 and 4,552,233, both by Klima, disclose sealed rotary drill bits which use more than one seal placed in seal grooves in the journal to prevent escape of lubricant from inside the cones and to provide a barrier to prevent entry of drilling debris. Klima U.S. Pat. No. '836 also discloses the use of a relief valve where when a predetermined pressure is exceeded, lubricant is conducted to the bottom of a seal groove to provide a lubricant function for an outer seal as well as to prevent the application of undue destructive pressure forces to an inner seal. In Klima U.S. Pat. No. '233, as the pressure of lubricant inside the cone increases due to heat, lubricant may exit a port and fill the space between seal rings and the journal. In both Klima patents, lubricant supplied to the seals is continuously lost into the environment. Since neither patent provides an internal reservoir for replenishing lubricant when lubricant is lost, the lubricant must be replenished by refilling the drill bit. Since lubricant is continuously lost, the drill bit must be refilled often, many times after each period of operation.
U.S. Pat. No. 4,225,144 by Zitz et al. discloses a way of sealing the gap between a cutting head and a cutting arm of a drilling machine used in mining. In this patent, an inner cavity is sealed in the outward direction by sealing elements of one type. An additional sealing element of a second type is formed by a lip seal. A pressurized grease conduit opens into space located between the two types of sealing elements and into labyrinth gaps. This grease conduit can be connected to a grease pump or grease press. The resistance of the flow of grease for the lip seal is smaller than the flow resistance for the first type of sealing elements. The sealing lip is arranged in such a direction that the grease emerges in an outward direction via the labyrinth gaps so that any dust particles having entered the sealing gap will be transported in the outward direction.
It is the object of the present invention to provide a sealing arrangement of two seals placed in seal grooves in the conical cutter separated by a circumferential seal gap filled with lubricant supplied from the bearings, where the lubricant has a tendency to flow past an outer seal in the outward direction, and where a separate reservoir holds a large enough supply of lubricant to replenish lubricant to the bearings to replace lubricant lost past the outer seal, so that the drill bit can be operated for long periods of time before requiring refilling. It is another object of this invention to provide the above sealing arrangement where lubricant having a lower penetration value than the bearing lubricant is first supplied to the circumferential seal gap, followed by bearing fluid also supplied to the gap. It is a further object of the present invention to provide for a sealing arrangement where the innermost seal is a hydrodynamic seal which carries lubricant from the bearings into the circumferential seal gap, but prevents migration of lubricant or contaminants from the gap into the bearings.